The Physiology Core supports comprehensive, state-of-the-art physiological characterization of bone and other musculoskeletal tissues. The Core is comprised of 3 "subunits" which are coordinated by the director. The services of the Core are very heavily subscribed, and it is the largest of the three scientific cores. The Histology and Histomorphometry Subunit provides high quality histologic and histomorphometric analyses of skeletal tissue. Recent initiatives have included the development of an in situ TUNEL assay, and new immunohistochemical stains in response to the needs of specific investigators. A recent external audit of the subunit concluded that the services being provided are of extremely high quality. The Biochemical Markers of Bone Turnover Subunit offers assays of bone turnover makers and serum PTH. Assays for media osteocalcin, calcium, phosphate, and alkaline phosphatase, in mineralizing bone cell cultures are new initiatives in the laboratory. The Bone Densitometry Subunit supports measurement of bone density by peripheral quantitative computerized tomography (pQCT) and by dual energy absorptiometry (PlXlmus) through an agreement with the Cell Core. The specific aims of the Core are to: 1) continue to provide the above summarized services to Center members in a coordinated and efficient manner, thereby extending the range and productivity of their work; 2) to offer training in these techniques to Center members and 3) to continue to develop and evaluate new methodologies relevant to the analysis of skeletal tissue in vivo and in vitro.